TAMPA — Downtown Tampa’s 87-year-old Laurel Street bridge will close for two weeks for repairs starting Monday. The bridge will reopen Oct. 18.

Drivers who use the bridge will be detoured onto Cass Street or North Boulevard.

The repairs weren’t planned for, said David Vaughn, the city’s contracts administrator.

They turned up during emergency repairs the city made earlier this year.

Inspectors with the Department of Transportation told the city a year ago the machinery that lifts the bridge has large cracks that allowed a gear to slip out of alignment. The damage was severe enough to prevent the bridge from rising to accommodate boat traffic.

The Tampa City Council approved a $1.9 million contract with Venice-based Coastal Marine Construction Inc. in January to replace bearings, switches and other electrical devices as well as install a new control panel and brake system.

While making repairs, crews discovered the area around a pin assembly connected to the bridge’s giant counterweight was in worse condition than they had expected, Vaughn said.

What was supposed to be a simple lane closure was expanded to a full bridge closure, Vaughn said.

Mayor Bob Buckhorn included another $1.3 million for the Laurel Street bridge in his 2014 budget. The funds come from the city’s local-option gas tax.

Tampa has eight drawbridges that cross the Hillsborough River between Hillsborough Avenue and Platt Street. They are all close in age. Two — Platt Street and Columbus Drive — were renovated last year.

The Laurel Street bridge is known as a rolling-lift bascule bridge. The span rises by pivoting on two toothed gears on the west side. A counterweight mounted above the roadway helps tip the bridge up and down.

The bridge was built in 1926 and rebuilt in 1969. It carries 5,240 cars a day. The Kennedy Boulevard bridge, by comparison, carries 38,500, according to the Department of Transportation.

The Coast Guard requires that the city’s drawbridges open to allow the passage of boats and barges too tall to pass under them safely.

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